Hi Nicolas and all,

Here's a new patch that adds a variable org-latex-custom-id-as-label to
control whether CUSTOM_ID should be used to generate labels during LaTeX
export.

Let me know what you think.  In particular, I wasn't sure if I should
provide more information in the defcustom statement beyond :group and
:type (like :package-version?).  Also, does the docstring represent the
trade-offs of using this variable well enough?

I wasn't sure how to get git format-patch to generate a single patch for
the changes between my branch and master (since there are now two
commits on my branch), so this was generated with git diff --patch.  If
you want me to send the commit message, etc. can you let me know how to
do this in whatever way is most convenient for you?